The present invention relates to a novel flame resisting agent suitable for improving the flame resistant property of a fiber consisting of chlorine-containing polymer as a main polymer ingredient, particularly a flame resisting agent which has a superior dispersibility in an aqueous spinning dope containing chlorine-containing polymer as a main polymer ingredient and gives an aqueous spinning dope having a superior stability, filtering property and spinning property, from which a fiber having a durable, superior flame resistant property can be obtained and to a process for preparing the same.
Recently, there has been a flame resistant property as one of the important properties commonly required for a variety of synthetic fibers. It has been known to give a flame resistant property to a synthetic fiber made of a chlorine-containing polymer by incorporating antimony trioxide into the polymer. However, antimony trioxide shows a poor dispersibility in an aqueous spinning dope and cannot give the fiber with a sufficient flame resistant property to be required for a flame resistant fiber.
Previously, the present inventors had found that, by incorporating stannic acid into an aqueous spinning dope containing chlorine-containing polymer and polyvinyl alcohol as main polymer ingredients, a durable, good flame resistant property could be obtained in a synthetic fiber spun from the spinning dope (U.S. Patent application Ser. Nos. 242,745 and 513,200). However, stannic acid was liable to lower the stability, filtering property and spinning property of an aqueous spinning dope in which stannic acid was incorporated, and as a result, the fiber spun from the spinning dope has a poor mechanical strength and it was difficult to produce the fiber in a stable condition.